In various computing devices and other systems, secret information known only to authorized users may be used for controlling access to the system. Methods for detecting and blocking unauthorized accessing attempts are known in the art. For example, U.S. Patent Application Publication 2006/0047955, whose disclosure is incorporated herein by reference, describes techniques related to protecting an application of a multi-application smart card against unauthorized manipulations. A system and method for guarding against unauthorized modifications includes partitioning the application into a plurality of basic blocks. For each basic block a check value is computed and remembered, wherein the check value is a function of data units of the basic block. During or prior to execution of the basic block, the check value is re-computed and verified to be the same as the remembered check value. If not, an error condition is indicated and a corrective action may be taken.
As another example, U.S. Pat. No. 7,996,911, whose disclosure is incorporated herein by reference, describes a memory card capable of preventing data leakage to a third party not having access authority, by imposing a limitation on the number of password authentications and automatically erasing the data. In a system comprised of a multimedia card and a host machine electrically connected to the multimedia card and controlling the operations of the multimedia card, a retry counter for storing the number of password authentication failures is provided, and the upper limit of the number of failures is registered in a register. When passwords are repeatedly entered once, twice, and up to n times, and the retry counter which counts the entries reaches the upper limit of the number of failures, the data is automatically erased so as not to leave the data in the flash memory.